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segments, which diminish successively in length. The next segment bears a pair of brackets, 

 representing the bases of the distal zooecia of the more typical stem-segments ; but the zooecia 

 themselves, as in the next following segments, have fallen off. The next segment, and all its 

 successors, bear two pairs of brackets, the proximal pair being situated more laterally than the 

 distal pair. Between the proximal brackets the cuticle has an oval fenestra, closed by membrane, 

 into which are inserted the ends of a linear series of short muscle-fibres l ), which originate in 

 the opposite wall of the stern-segment (figs 3, 4). It seems clear that the contraction of these 

 fibres must increase the pressure of the fluid in the cavity of the segment. This presumably 

 increases the turgidity of the segment, and probably makes it sufficiently rigid to withstand the 

 strain caused by the contraction of the muscles which move the zooecia. Occasional fenestrae 

 of more irregular form may be seen on other parts of the wall of the stem-segments. 



Fifteen stem-segments have been omitted, and the upper part of the figure shows the 

 remainder of the stem. The deciduous zooecia have disappeared from all the segments omitted 

 in the figure, with the exception of one which bears a single zooecium, and from the two lower 

 segments of this upper part of the stem ; and some of the succeeding segments do not retain 

 the full number of zooecia. But the constant occurrence of two pairs of brackets may be taken 

 as a sure indication that each of these segments has borne its full number of zooecia at some 

 time during the growth of the stem. Xear the distal end, each segment has four zooecia. 



The typical arrangement can be seen more clearly in figs 1, 2, showing the growing 

 ends of two sterns under a higher magnification. The zooecia originate near the tip of the stem 

 as small rounded outgrowths, two pairs of which belong to each stern-segment. It is noteworthy 

 that in an early stage of growth (fig. 1) the proximal zooecia are directed towards what may 

 be called the back of the stem; i. e., the surface opposite to the one on which the brackets of 

 the distal zooecia are situated. In the older segments all the zooecia may be directed towards 

 the front of the stem ; but it may be assumed that this position is not constant, and that there 

 is a considerable range of movement in the fully grown zooecia. 



The zooecia are attached by a narrow base, where a joint is present. When fully grown 

 they are subcylindrical, and are terminated by an orifice, which is quadrangular in shape. The 

 vestibule is short : — ■ a character which appears to be correlated, in the non-incrusting Ctenostomes 

 in general, with a feeble development of the collar. This structure is certainly very delicate in 

 the present species. The tentacles, eight in number, remain unbent during retraction, and the 

 alimentary canal similarly retains its U-like form (fig. 3). The oesophagus is short. The parietal 

 muscles are delicate. 



The rootlets are well chitinised and may be straight, sinuous or geniculate at intervals; 

 doubtless in correlation with the nature of the substratum. At the points from which the erect 

 sterns arise, several internodes may be crowded together. In a particular case (fig. 6) the 

 arrangement is as follows : — a rootlet (r. 1 ) gives rise to two successive internodes, with no 

 interval between them. A diaphragm occurs at the commencement of the first internode (e. 1 ), 



1) Muscle-fibres of a similar nature have been described by Waters (1910, pp. 239, 250) in Mimosclla graa'/is, Hypophorilla 

 (fide EHLERS), Farrella rcpais and Valkeria uva. Joi.iet (1877, "Contr. hist. Bry. cötes de France", Arch. Zool. Exp. VI, p. 293) bad 

 previously described them in Lagenclla nutans (see the following species) and in Valkeria. 



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